1. Technical Field
This invention relates to the construction of barrages that can be used to extract energy from tidal or current flows for the generation of electricity.
2. Description of the Related Art
There have been many proposals for using tidal flow or current flow in a body of water for generating electricity as a non-polluting approach to power generation. Such systems have involved the use of a vane which can be caused to oscillate by the flow, a mechanical transmission system converting this into rotary motion. Such systems face problems such as being mechanically complicated, requiring tuned behavior and are often unable to extract energy from other types of motion.
Other systems feature a large underwater propeller analogous to a windmill but for water instead of wind flows. For the swept disc to gain exposure to the maximum incident current energy, the blades have to be very long which in turn requires sophisticated design and materials to accommodate the stresses at the blade root.
Offshore tidal barrages have been proposed to concentrate the incidental energy of a large cross-section of water flow by trapping the flow behind a containing wall and funneling it through turbines of much smaller cross-sectional area, as in a conventional dam. Such barrages, typically across a tidal estuary, are very expensive and environmentally disruptive.
One common problem for all these systems is to address a sufficiently large cross-section of the ocean or other body of water for power generation to be possible on an industrial scale. Furthermore, end or edge effects can make it easier for the flow to go around any structure positioned in the flow to extract energy from it rather than to pass through the energy extraction system. This problem can be lessened by making an installation very large but this in turn can lead to further complexity and expense and may be beyond the limits of current engineering capability.
WO 2008/015047 discloses improved apparatus for converting energy from wave or current flows wherein a series of pipes are arranged such that venturi are defined. Water flow between these pipes causes the venturi to act as pumps drawing water up through the pipes which are fed by a manifolding flow conduit and driving an impeller. The series of pipes are arranged to form arrays with vertical planes which in turn are mounted on the sea bed to form barrages.